Mechanical Unfoldons as Building Blocks of Maltose-binding Protein

Journal of Molecular Biology, 2008, doi:10.1016/j.jmb.2008.02.025, Volume 378, Issue 2, Pages 447–458 published on 25.04.2008
Journal of Molecular Biology, online article
Identifying independently folding cores or substructures is important for understanding and assaying the structure, function and assembly of large proteins. Here, we suggest mechanical stability as a criterion to identify building blocks of the 366 amino acid maltose-binding protein (MBP). We find that MBP, when pulled at its termini, unfolds via three (meta-) stable unfolding intermediates. Consequently, the MBP structure consists of four structural blocks (unfoldons) that detach sequentially from the folded structure upon force application. We used cysteine cross-link mutations to characterize the four unfoldons structurally. We showed that many MBP constructs composed of those building blocks indeed form stably folded structures in solution. Mechanical unfoldons may provide a new tool for a systematic search for stable substructures of large proteins  

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